Abstract

A conceptual and methodological framework has recently been developed from ablending of a traditional dual-task methodology and a dynamical perspective oncoordination. Specifically, pattern stability has been shown to be a good predictor ofVU)attentional demands (i.e., central cost) needed for maintaining coordination. One of theimportant assumptions is that the allocation of attentional resources can modify thecoupling strength of interlimb coordination. Within this original framework that blendstwo different theoretical approaches with attention as an intervening variable modifyingbehavioural patterns, the present research further investigated at the behavioural andneurophysiological levels, the central cost of dynamical coordination patterns.Two experiments were carried out in the Phase 1 of the present research. The firstexamined whether previous findings obtained with bimanual coordination patterns couldbe extended to coordination patterns involving non-homologous limb combinations.Consistent with previous results, coordination stability and probe RT (i.e., a measure ofattentional load) were found to co-vary. Furthermore, it was shown that temporal aspectsof the coordination task were selectively modulated through attentional prioritisationwithout affecting the spatial aspects of the task (i.e., movement trajectories).Following evidence from Experiment 1 of dissociation between the temporal andspatial dimensions of interlimb coordination, the second experiment explored whetherattentional focus could selectively modulate the spatial aspects of the interlimbcoordination task without affecting the temporal coupling between the limbs. Experiment2 showed that when the spatial aspects of the interlimb coordination task were prioritised not only the movement trajectories but also the temporal variability of the interlimbcoordination task were modulated. Interestingly, attentional focus to the spatialdimension of interlimb coordination abolished the inherent performance asymmetriesusually observed between the limbs (i.e., spontaneous performance differences betweenthe left-hand and the right-hand and an ann and leg).IXPhase 2 of this research explored the neural correlates of dual-task performanceinvolving an interlimb coordination and probe RT task. Single-pulse transcranialmagnetic stimulation (TMS) was employed in a series of three experiments to specificallyassess the excitability of corticospinal pathways during single- and dual-taskperformance. The first experiment examined the time course of corticospinal excitabilityof the tibialis anterior (TA) during the RT interval to a secondary task probe stimuluswhile simultaneously maintaining bimanual in-phase and anti-phase coordination modes.Although corticospinal excitability of the TA did not differ between the in-phase andanti-phase coordination modes, a large increase in corticospinal excitability was observedbetween single-task and dual-task performance.The second experiment examined whether the elevated corticospinal excitabilityduring dual-task performance was a 'motor effect' reflecting increased corticalexcitability associated :.vith the performance of the continuous bimanual coordination taskor it whether reflected the concurrent performance of two tasks (i.e., a dual-task effect).The results showed that the elevation of corticospinal excitability was due, in part, to theproduction of bimanual movements. However, a further increase in corticospinalexcitability also occurred in the dual-task condition. Thus, the increased corticospinalexcitability appeared to reflect a neural process related to the concurrent performance oftwo tasks.xA final experiment tested whether the increased corticospinal excitability was ageneral signature of dual-task performance or specific to interactions within the motorcortex. Dual-task conditions involving either a primary motor task or a primary cognitivetask (i.e., tone counting) combined with probe RT were compared. Results showed thatincreased corticospinal excitability was not a general effect of dual-task performance, butspecific to dual-task situations involving motor tasks.Overall, the findings of the experiments conducted in this research exploringattention and coordination dynamics provided further support to the view that attentionalallocation impacts on the coupling strength between the limbs and affects both thetemporal and spatial dimensions of interlimb coordination. Furthermore, at the neurallevel, dual-task effects showed different neural manifestations for structural interferenceand capacity interference.